In the prior art, the drill chuck is provided with a drill body, a clamping jaw and a nut. By rotating the nut, the clamping jaw is driven to move forward or backward to make the drill chuck to clamp or loosen the drill tool. The self-locking structure of the drill chuck is a structure that can prevent the drill tool from being loosened by the reaction force during working. Generally the part with a spring leaf is fit with teeth on the drill body. For the existing self-locking drill chuck, the spring leaf should have more functions including self-locking, and during the whole or most stroke when the nut of drill chuck is rotating in the clamping direction, the rotating sleeve needs to be driven by the spring leaf and the spring leaf has too high load, which easily causes the failure of self-locking functions of the self-locking drill chuck. In addition, the spring leaf is made in a normally open state of sprung outwardly in most self-locking drill chucks. The locking end of the spring leaf is pressed between teeth forcibly by the cam surface on the rotating sleeve which influences the connecting structure of the rotating sleeve; and it is always subject to a centrifugal force during working, this kind of structure has influence on the stability of the self-locking function.